The fuel cell has been proposed as a clean, efficient, and environmentally responsible power source for various applications. A plurality of fuel cells may be arranged to form a fuel cell stack capable of powering an electric vehicle. One example of the fuel cell is a Proton Exchange Membrane (PEM) fuel cell. In the PEM fuel cell, hydrogen is supplied as a fuel to an anode and oxygen is supplied as an oxidant to a cathode. A common technique for storing hydrogen is in a lightweight, high pressure vessel resistant to puncture. High pressure vessels containing the compressed hydrogen gas must have a desired mechanical stability and integrity that militates against a rupture or bursting of the pressure vessel from the internal pressure. It is also typically desirable to make the pressure vessels on vehicles lightweight so as not to significantly affect the weight requirements of the vehicle.
Known high pressure vessels include at least one thermally activated safety valve or pressure relief device (PRD). The PRD is located at a boss or an end of the high pressure vessel that houses various valves, pressure regulators, piping connectors, excess flow limiters, etc. for allowing the pressure vessel to be filled with the compressed hydrogen gas. The PRD may also be located at another opening in the pressure vessel, though the PRD generally is disposed at one or both ends of the pressure vessel. The PRD is useful when the pressure vessel is exposed to high temperatures. More than one PRD may be used where high temperatures might occur at a localized area apart from the location of the single PRD. One known PRD includes an elongated, fragile bulb coupled to an ignitable cord which transfers heat to the PRD from remote areas of the vessel. When heated to a predetermined temperature, the bulb breaks, thereby opening the venting aperture and actuating the PRD. However, heat transfer to the PRD by the ignitable cord is not suitable in certain applications and occasionally unpredictable, which could result in an undesired rupture or bursting of the pressure vessel. Further, the elongated bulb requires a large package size, as well as includes a significant volume of temperature sensitive material to be heated for actuation of the PRD.
Accordingly, there is a continuing need for a PRD which can be installed in a high pressure vessel for use with a fuel cell stack. Desirably, the PRD includes a trigger mechanism which minimizes a package size, a manufacturing cost, and an activation period of the PRD.